1. Field
The technology of the present application relates generally to the field of a blow-down system for a variable frequency drive compressor unit.
2. Background
When a compressor stops it blows down the pressure in the sump. If there is a demand for air, the compressor will need to start up again and build pressure back up in the sump before it can deliver air to the air system. In order to save energy, compressed air can be saved in a sump when the compressor stops. If the compressor does not start up for a while, the sump can be dumped, i.e., “blown-down,” by using a release value, such as, for example, a solenoid, in a separator tank. If the pressurized air is left in the sump, it can begin to leak. As a result, conventional systems typically will either not have any blow-down when the compressor unit shuts down or only have a blow-down whenever the compressor unit stops.
A conventional variable frequency drive (VFD) compressor unit can cycle (i.e., shutdown and start-up) with a high frequency when the compressed air demand is low. With every shutdown, the sump is normally blown-down. In other words, the compressed air, which is typically about, 100 to 150 psi inside sump, is evacuated to atmosphere. This blow-down causes energy loss, lubricant loss, and it is not environmentally friendly.
A blow-down is not necessary for a VFD compressor unit to restart. The VFD compressor unit can start up under full sump pressure. When the VFD compressor unit is blown-down, the compressed air inside the VFD compressor unit can cause moisture condensation, which can cause compressor unit parts (e.g., bearings) to rust and can reduce the service life of the compressor unit and lubrication fluid.
What is desired is a compressor unit that minimizes the amount of blow-downs in order to save energy, be more environmentally friendly, and extend the life of the compressor unit and its components.